Japanese Patent Application Publication No. 2012-202382 A discloses a technology for supplying an engine with fuel from a fuel pump unit configured to change a discharge amount of fuel per unit time. A supply path between the fuel pump unit and the engine includes a check valve. The check valve opens in a fuel supply direction from the fuel pump unit toward the engine, and closes in the opposite direction thereto. Connected to the supply path is a pressure regulator.
The pressure regulator includes an introductory passage connected to a side of the supply path downstream of the check valve, an operating pressure supply and discharge passage connected to a side of the supply path upstream of the check valve via a three-way valve, and a discharge passage through which the fuel is discharged into a fuel tank. The three-way valve switches between a supply state in which the operating pressure supply and discharge passage communicates with the side of the supply path upstream of the check valve and a discharge state in which the operating pressure supply and discharge passage communicates with the inside of the fuel tank. The introductory passage, the operating pressure supply, and the discharge passage communicate with one another when a valve member opens, and are isolated from one another when the valve member closes. The valve member receives pressure of fuel inside of the introductory passage and pressure of fuel inside of the operating pressure supply and discharge passage when the three-way valve is in the supply state, and receives pressure of fuel inside of the introductory passage when the three-way valve is in the discharge state. As a result, in a case where the three-way valve is in the supply state, the valve member opens with the pressure inside of the supply path being comparatively low. The above technology is a technology for adjusting the pressure inside of the supply path by switching the three-way valve between the supply state and the discharge state.